Method of removing propane and other hydrocarbons from gases



K. JAEGER Swpt w, M?

METHOD OF REMOVING PROPANE AND OTHER HYDROCARBONS FROM GASES 2 Sheets-$heet 1 Filed Oct. 13, 1965 lvefl for" KA RL (J14 6.51?

Sept. 19, 17 K. JAEGER METHOD OF REMOVING PROPANE AND OTHER HYDROCARBONS FROM GASES Filed Oct. 13, 1965 2 Sheets-Sheet 2 Curve III:

95 Decrease of C H content INVENTOR:

FIGURE 4 a 50 M0 N0 20H 250 lm K Temperature 1 Z" of Air OXIDATIVE DECOMPOSITION OF 60 IO PPM PROPANE IN AIR UNDER VARYING CONDITIONS Curve 1 Manganese dioxide fig without ozone Curve II Ozone without manganese dioxide Ozone and manganese dioxide KARL U'MEGER ATTORNEY United States Patent Ofifice 3,342,545 Patented Sept. 19, 1967 3,342,545 METHOD OF REMOVING PRCWANE AND OTHER HYDROCARBQNS FROM GASES Karl Jaeger, Munich, Germany, assignor to Linde A.G., Wieshaden, Germany Filed Oct. 13, 1965, Ser. No. 505,096 Claims priority, application Germany, Oct. 14, 1960, G 30,704 13 Claims. (Cl. 23-4) This invention is a continuation-in-part of copending application Ser. No. 143,682, filed Oct. 9, 1961, and now abandoned.

The present invention relates in general to the removal of organic molecules from a gas, more particularly, to a process for removing hydrocarbons from air prior to the separation of the air into its major components by a low temperature rectification process.

In order to eliminate the danger of explosion in plants for the separation of air, it has been known to burn the hydrocarbons in the air by means of an appropriate catalyst prior to introducing the air into the low temperature rectification installation. For this combustion process it was necessary to heat the air to a temperature of 150 to 350 C. depending on the catalyst used and the degree of purity required of the incoming air. Subsequently, it was necessary to cool the air down to the ambient temperature. When noble metals were used as catalysts, the air containing hydrocarbons, particularly propane, could not have its temperature reduced much below 200 C. in order to avoid a dangerous accumulation of hydrocarbons in the installation.

In order to remove the hydrocarbons from the air the usual practice was to heat the air in countercurrent heatexchangers or regenerators and subsequently cool the air after the combustion of the hydrocarbons. However, this practice had the disadvantage in that the costs of the installation are too high for economic operation.

Another process was devised wherein the air was heated by means of a combustible gas or by a flame burning in the air and after the catalytic reaction the air was cooled down to the ambient temperature. This process also was necessary to provide air heaters as well as vapor generators in addition to the combustion or contact chamber in which the hydrocarbons were burned. In addition,

some provision had to be made to either utilize or dissipate the energy of the steam created therein.

It is therefore an object of this invention to provide a novel and improved process and apparatus for the removal of hydrocarbons by combustion from air before the air is introduced into a low temperature rectification installation.

It is a further object of this invention to provide a method and apparatus for the removal of hydrocarbons from air by burning the hydrocarbons at the temperature resulting from the compression of air to the pressure necessary for introduction into the low temperature rectification installation without addition-a1 heating of the air.

A still further object is to remove organic molecules from contaminated air in general, for example, from engine exhaust gases.

Upon further study of the specification and claims other objects and advantages of the present invention will become apparent.

To attain the objects of this invention, a system is provided based on the discovery that contaminated air can be purified at relatively moderate temperatures, by destroying the organic molecules therein by treatment with ozone in the presence of a catalyst.

With respect to the utilization of this invention in low temperature air separation systems, the disadvantages of the prior art as described above are eliminated and the objects of the present invention are achieved by bringing the air into contact with ozone in the presence of a catalyst after the air has been heated by compression. By mixing the air with ozone in the presence of a catalyst, the increase in temperature resulting from the compression of air is suflicient for the combustion of the hydrocarbons. Accordingly, no additional equipment is necessary for heating and recooling the air and accordingly there are no heat losses resulting from this heating and cooling.

Thus, one embodiment of the process of the present invention essentially comprises initially compressing the air which is to be separated to the pressure necessary for introducing the air into the rectification installation. The compressed air .is then passed into a chamber containing a catalyst and which is connected with a source of ozone. This ozone can be produced in a manner known per se from pure oxygen and then blown into the stream of compressed air. The ozone can also be produced from the oxygen contained in the compressed air. For best results, the quantity of ozone is at least 1.5 times, preferably about five times, the stoichiometric quantity necessary for effecting the reaction.

The reaction equation is represented by the following:

With respect to the type of catalyst that can be employed in this invention, manganese dioxide is preferred because of its low cost and good efficiency even at relatively low temperatures. On the other hand, if catalyst cost is not so important for a particular application, use can also be made of noble metal catalysts such as, for example, palladium or platinum in their conventional catalytic forms. Moreover, catalysts functioning in a substantially equivalent manner can also be employed.

In contrast to these catalysts, activated charcoal is most disadvantageous in this respect. Activated charcoal is known to dissipate ozone very quickly, so if organic molecules are passed over activated charcoal together with ozone, the latter is dissipated in so short a time that an appreciable oxidation of organic molecules cannot take place.

This invention is broadly applicable for the oxidation of all types of organic molecules, particularly those having up to about 10 carbon atoms to yield reaction products of CO and H 0, with NO, N0 and S0 also being possible-depending on the constitution of the organic molecule.

The invention is particularly useful for the oxidation of saturated hydrocarbons having 1-l0 carbon atoms, which are ordinarily more diflicult to oxidize, especially propane, at relatively moderate temperatures.

In general the process of this invention can be conducted by treating the contaminated air with the catalyst and ozone at preferably 25280 C. For noble metal catalysts the upper limit is more preferably about 200 C. With respect to the utilization of this invention in low temperature air separation processes, however, such high upper limits are to be avoided because of refrigeration energy requirements; consequently in this embodiment of the invention, the upper limit is advantageously about 150 C. for the manganese dioxide catalyst, and about C. for the noble metal catalysts. It is important to note at this point that it is only by treating the impurities with ozone in the presence of a catalyst that a suflicient percentage of the impurities can be destroyed at such relatively low maximum temperatures. As minimum reaction temperatures for the removal of hydrocarbons from air, about 25 C. is preferred for noble metal catalysts, whereas for manganese dioxide, a minimum temperature of about 30, preferably at least 70 and more preferably at least 80 C., and most preferably a reaction temperature of about 90l30 C. can be used.

From a general standpoint this invention is useful for destroying organic molecules in varying concentrations in all types of gases ranging from low concentrations in ordinary air to high concentrations in exhaust gases. As a rule of thumb, the contaminants will not exceed by volume of the gas.

With respect to low temperature processes, this invention is of particular value when the concentration of each hydrocarbon impurity does not exceed ppm, the usual concentration being about 2 ppm. In any event, the reaction between the impurity and ozone in the presence ofa catalyst takes place very quickly, the desired contact time being only on the order of seconds.

In the event the hydrocarbons are not sufiiciently removed in a single application of the process, the process can be repeated several times. This can be done by adding fresh ozone to the hot stream of air after the air has 7 passed the catalyst. It is particularly eifective to mix the air containing hydrocarbons and the ozone in the presence of the catalyst or within the catalytic material itself. In other words, it is preferred that a substantial percentage, advantageously at least 40%, more beneficially at least 60%, and desirably 100% of the decomposition reaction takes place in the presence of the catalyst.

In order to prevent any excess ozone from entering the low temperature rectification installation after this reaction, the residual ozone (about 0.1 to 10% of the starting concentration) is dissipated by passing the air over a suitable material such as a bed of iron ore, activated charcoal, or platinum black. The temperature range for the residual ozone decomposition reaction is from room temperature up to the temperature at which the' oxidation of the organic molecules is performed.

In those applications where the air is to be washed before entering the low temperature rectification installation, a suitable substance for decomposing the ozone may be added to the washing agent.

In order to increase the speed and efficiency of the reaction wherein the hydrocarbons are removed from the air, the air can be heated to a higher temperature after it has been compressed. Usually, in air separation plants the gas leaving the turbocompressor has a temperature of 90 to 100 C.

Other objects and advantages of this invention will be apparent upon reference to the accompanying descrip tion when taken in conjunction with the following drawings, wherein:

FIGURE 1 is a schematic view of the apparatus of the present invention showing the air separation installation and a single oxidation stage;

FIGURE 2 is a schematic view similar to that of FIG- URE 1 but showing three oxidation stages combined in a single unit;

FIGURE 3 is a schematic view of a modification of the present invention wherein the air is further heated after being compressed; and

FIGURE 4 is a graph which illustrates the synergistic effect achieved when oxidizing propane with ozone in the presence of :manganese dioxide.

Returning now to the drawings wherein like reference symbols indicate the same parts throughout the various views, the invention will first be described with particular reference to FIGURE 1. In FIGURE 1 the air which is to be separated by the low temperature rectification process is entered through a conduit 1 and compressed in a compressor 2 to the pressure necessary for the air separation installation which is connected in series there with. The compressed air is then passed into ozone chamber 3 which is connected to a source of ozone through the conduit 9. A contact chamber 4 having manganese dioxide therein as a catalyst is then connected in series to the chamber 3. A bed of iron ore 5 is con- 4- nected to the contact chamber 4 and a recooler 6 connected to the bed 5. A conduit 7 then connects the recooler 6 with a conventional low temperature rectification air separation installation 8.

In carrying out the process in the apparatus as described in FIGURE 1, the air is compressed in compressor 2 to a pressure of approximately 6 atmospheres and accordingly is heated to a temperature of about C. This air contains, for example, 2 ppm. each of acetylene, propane, propylene, and butane. The compressed air is then passed into the ozone chamber into which ozone is introduced through the conduit 9 to be mixed with the heated air. The ozone is conventionally produced by passing a silent electrical discharge through pure oxygen or by the action of ultraviolet radiation. For the aforementioned quantity of hydrocarbons in the air approximately 350 p.p.m. of ozone are introduced. The quantity of ozone is about five times the stoichiometric quantity necessary for effecting the reaction.

One portion of the hydrocarbons is immediately removed by combustion and a further part of the hydrocarbons is burned in the contact chamber 4. The contact chamber 4 contains manganese dioxide (MnO- in a quantity corresponding to a space velocity (weight rate of flow per hour and volume of contact) of approximately 4000 Nm. /h./m. More than of the aforementioned hydrocarbons are burned at the end of the contact chamber 4.

The air is then passed over the bog iron ore bed 5 to remove the excess ozone therein. The air is then passed through the recooler 6 and through the conduit 7 into the low temperature air separation installation 8. This installation may be operated by means of reversible heatexchangers or regenerators in order to further cool the air to be separated and to remove carbon dioxide and water from the air. If desired, the air may also be washed for removing the impurities therefrom before entering the installation 8. A sodium sulfite solution may be added to the washing agent to also effectively decompose any excess ozone contained in the air.

The apparatus illustrated in FIGURE 2 is essentially the same as that shown in FIGURE 1 except that the ozone chamber, the contact chamber and the iron ore bed are combined in a single unit indicated at 10. In this unit the compressed air discharged from the compressor 2 is alternatingly passed through ozone chambers 13 and contact chambers 14 having catalytic material therein. A bed of bog iron ore 15 is provided after the last contact chamber. In this embodiment electrical discharge gaps are provided in the ozone chamber whereby the ozone is produced in the chambers from the oxygen contained in the air. It is, of course, possible to introduce ozone into the chambers 13 from an external source of ozone as described in the embodiment of FIGURE 1.

The process of removing the hydrocarbons from the air is conducted in the same manner with the apparatus of FIGURE 2 as previously described in connection with FIGURE 1.

Proceeding next to FIGURE 3 there is shown an apparatus according to the present invention wherein the air is heated to a higher temperature after the air has been compressed. In addition, this apparatus provides two regenerators whose functions can be reversed so that the entire process is continuous although the regenerators alternatingly perform their functions. The various components of the installation are interconnected by valves 11 and 12 with the valves 11 being shown in the open position for fiow of the air through one regenerator and the valves 12 being shown in the closed position.

In this position of the valves, the air is discharged from the compressor 2 into a regenerator 16 which has a bed of bog iron ore 15 or rusty iron at the one end thereof for dissipating excess ozone. The air then flows through a reheater 18, an ozone chamber 13 and a catalyst contact chamber 4. The heated air from which the hydrocarbons have been removed then flows through the regenerator 17 and is further cooled in the recooler 6. The cooled air is then conducted through the conduit 7 to the low temperature air separation installation.

After a predetermined time interval the positions of the valves 11 and 12 are reversed and the functions of the two regenerators 16 and 17 are reversed.

Referring now to FIGURE 4, it is seen that the utilization of ozone in the presence of manganese dioxide permits the use of much lower temperatures for the oxidative decomposition of propane. The data was obtained by experiments carried out in the following manner.

In a steel cylinder air was mixed with propane so that the air contained exactly ppm. propane. The mixture was then passed through a tube which was provided with manganese dioxide and surrounded by an oil bath of a definite temperature (curve I) or through an ozonizer (curve II) or first through the ozonizer and then through the tube containing manganese dioxide (curve III). After having passed the ozonizer and/ or the catalyst the amount of gas was measured in a metering device and its content of propane analyzed by means of gas chromatography.

As can be seen from the diagram, the content of propane diminished considerably when passing the mixture over the ozonizer and the catalyst in a temperature range which lies around 100 C., the content of propane being diminished by almost two powers of ten.

The comparative oxidation of ethane shows similar characteristic results. Higher saturated hydrocarbons, on the other hand, decompose even more readily.

Thus it can be seen that the present invention provides a process and apparatus for the elfective removal of hydrocarbons, particularly saturated hydrocarbons such as propane, from air.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and Without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Consequently, such changes and modifications are properly, equitably, and intended to be, within the full range of equivalence of the following claims.

What is claimed is:

1. A process of gas purification which comprises treating a contaminated gaseous stream with ozone in the presence of a catalyst selected from the group consisting essentially of manganese dioxide, said gaseous stream containing contaminants comprising propane, said propane being decomposed to essentially CO and H 0, said catalyst functioning to increase the rate of decomposition of said propane.

2. A process as defined by claim 1 wherein the treating step is conducted at 25-280 C.

3. A process as defined by claim 1 wherein all of the ozone and all of the contaminated gaseous stream are contacted with each other in the presence of the catalyst so that all reactions between the ozone and the propane are conducted in the presence of the catalyst.

4. A process for removing propane from air by combustion prior to the separation of air by low temperature rectification, and comprising the steps of compressing air containing propane to the pressure at which the air is to enter a low temperature rectification installation to raise the temperature of the air, mixing ozone with the heated air, and burning the mixture of heated air and ozone at 30*15 0 C. in the presence of manganese dioxide catalyst.

5. A process as defined by claim 4 wherein the burning temperature is -150 C.

6. A process as defined by claim 4 wherein the burning temperature is -150" C.

7. A process as defined by claim 4 wherein the burning temperature is 130 C.

8. A process as defined by claim 4 wherein all of the ozone and all of the contaminated gaseous stream are contacted with each other in the presence of the catalyst so that all reactions between the ozone and the propane are conducted in the presence of the catalyst.

9. A process as defined by claim 7 wherein all of the ozone and all of the contaminated gaseous stream are contacted with each other in the presence of the catalyst so that all reactions between the ozone and the propane are conducted in the presence of the catalyst.

10. In a process for removing propane and other hydrocarbons from air prior to the separation of air by low temperature rectification under pressure, the improvement which comprises the steps of compressing the air to that pressure at which the air enters the low temperature rectification zone, thereby raising the temperature of the air to above ambient temperature; adding ozone to said heated compressed air in a concentration of at least 1.5 times the stoichiometric quantity for effecting a reaction between said ozone and hydrocarbons in said air; reacting the ozone and hydrocarbons in the absence of a catalyst at 60150 C. thereby removing a portion of said hydrocarbons by combustion; and then contacting the resultant ozone and air stream with a manganese dioxide catalyst to remove additional hydrocarbons including a major part of said propane initially present in the air by combustion; and fractionating the resultant compressed air by a low temperature rectification process.

11. A process as defined by claim 10 wherein at least 40% of the combustion of said hydrocarbons takes place in the presence of the catalyst.

12. A process as defined by claim 10 wherein at least 60% of the combustion of said hydrocarbons takes place in the presence of the catalyst.

13. A process as defined by claim 10, comprising the further step of treating the resultant air having burned hydrocarbons therein with a substance different from said catalyst and capable of dissipating any residual ozone.

References Cited UNITED STATES PATENTS 1,602,404 10/ 1926 Frazer 232 2,700,648 l/1955 Thorpe et a1 23222 2,809,881 10/1957 Grosse et al. 23221 2,965,439 12/1960 Anderson et al. 232 3,151,943 10/ 1964 Fujimoto et al. 23222 OTHER REFERENCES Mellor: A Comprehensive Treatise on Inorganic and Theoretical Chemistry, Longmans, Green & Co., New York, N.Y., volume 10, 1930, page 265.

OSCAR R. VERTIZ, Primary Examiner. EARL C. THOMAS, Examiner. 

4. A PROCESS FOR REMOVING PROPANE FOR AIR BY COMBUSTION PRIOR TO THE SEPARATION OF AIR BY LOW TEMPERATURE RECITIFICATION, AND COMPRISING THE STEPS OF COMPRESSING AIR CONTAINING PRPANE TO THE PRESSURE AT WHICH THE AIR IS TO ENTER A LOW TEMPERATURE RECTIFICATION INSTALLATION TO RAISE THE TEMPERATURE OF THE AIR, MIXING OZONE WITH THE HEATED AIR, AND BURNING THE MIXTURE OF HEATED AIR AND OZONE AT 30-150*C. IN THE PRESENCE OF MANGANESE DIOXIDE CATALYST. 